1. Field of the Invention
The present invention relates to a micro-electromechanical device having a movable part and, in particular, pertains to a micro-sensor, micromachine or the like.
2. Description of the Related Art
With the development of production process in the field of semi-conductors, such as LSIs, there are widely used highly miniaturized devices equipped with semi-conductors in various technical areas, as pressure sensors, velocity or acceleration sensors and the like. Also, based on the production process for such miniaturized devices, research and development are actively conducted with respect to micro-electromechanical devices or so-called micromachine.
As known in the art, micro-electromechanical device typically includes a substrate which is comprised of silicon or the like, and a movable functional part in the form of cantilever, diaphragm or the like, which has been formed on the substrate by micromachining process, so that the movement of the functional part relative to the substrate achieves the desired function of the device. This type of micro-electromechanical device often suffers from stiction, i.e., a phenomena by which the functional part is fixedly adhered to the substrate and the desired movement of the functional part becomes impossible to achieve, thereby causing malfunction or failures of the device. It is generally considered that stiction is caused during production or use of the device, when moisture in a space between the substrate and the functional part evaporates and a surface tension therebetween causes the functional part to be attracted and fixedly adhered to the substrate. It is highly desirable to prevent occurrence of stiction and/or achieve a satisfactory stiction recovery once stiction has occurred.
There have been proposals for overcoming the stiction problem of micro-devices, and reference may be had to Appl. Phys. Lett. 68(2), pp. 197-199, 1996; Int. J. Heat Mass Transfer, Vol. 39, No. 15, pp. 3181-3186, 1996; as well as Transactions of the Japan Society of Mechanical Engineers, Vol. 69, No. 609, pp. 253-258, 1997. According to such proposals, the movable part of a miniature device, which has been subjected to stiction, is irradiated by ultrashort-pulse laser having a pulse width of 1 picosecond (10.sup.-12 sec.), such that the energy of the laser separates the movable part from the substrate to achieve the stiction recovery. However, besides that the laser device to be used is expensive, it is difficult to apply the proposed method to a micro-device which is hermetically enclosed in a package.